How do you build a Singleton in Dart?

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Thanks to Dart’s factory constructors, it’s easy to build a singleton:

class Singleton {
  static final Singleton _singleton = Singleton._internal();

  factory Singleton() {
    return _singleton;
  }

  Singleton._internal();
}

You can construct it like this

main() {
  var s1 = Singleton();
  var s2 = Singleton();
  print(identical(s1, s2));  // true
  print(s1 == s2);           // true
}

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